closures_and_methods.rb

# http://www.skorks.com/2010/05/closures-a-simple-explanation-using-ruby/

# "In computer science, a closure is a first-class function with free variables that are bound in the lexical environment."
#
# "A closure is a function that is said to be "closed over" it’s free variables"
#
#
# * You can pass it around like an object (to be called later)
#
# * It remembers the values of all the variables that were in scope when the function was created. It is then able to
#   access those variables when it is called even though they may no longer be in scope.

#######################################################################################################################
# - Spy -
#
# Responsibility of a spy is to collect messages
#
#######################################################################################################################
class Spy

  attr_accessor :messages

  def initialize
    self.messages = []
  end

  def overhear(message)
    puts "Spy: ..."
    messages << message
  end

  def report
    messages.each do |message|
      puts "Pssst! spied person said: '#{message}'"
    end
  end
end

class Journalist

  attr_accessor :messages

  def initialize
    self.messages = []
  end

  def note(message)
    puts "Journalist: Mhm"
    messages << message
  end

  def report
    messages.each do |message|
      puts "Dear readers! #{message}"
    end
  end
end

class Friend

  attr_accessor :messages

  def hear(message)
    puts "Friend: I am so happy! #{message}"
  end
end

#######################################################################################################################
# Person
#
# Person reports its thoughts to all that want to listen
#######################################################################################################################

class Person

  attr_accessor :report_channels

  def initialize
    self.report_channels = []
  end

  def add_report_channel(callback)
    report_channels << callback
  end

  def say(message)
    report_channels.each { |e| e.call(message) }
    nil
  end
end

def bootstrap
  spy        = Spy.new
  journalist = Journalist.new
  friend     = Friend.new

  magda = Person.new

  name = "Magda"

  # Callback using Proc
  _proc = Proc.new { |message| journalist.note("#{name} said: #{message}") }

  # Callback using lambda
  _lambda = -> (message) { friend.hear("#{name} said: #{message}") }

  # Callback using bound method (not a closure)
  meth = spy.method(:overhear)

  magda.add_report_channel(_proc)
  magda.add_report_channel(_lambda)
  magda.add_report_channel(meth)

  [magda, spy, journalist, friend]
end